440 MYOLOGY 



border and upper surface of the lateral third of the clavicle; from the lateral margin 

 and upper surface of the acromion, and from the lower lip of the posterior border 

 of the spine of the scapula, as far back as the triangular surface at its medial end. 

 From this extensive origin the fibers converge toward their insertion, the middle 

 passing vertically, the anterior obliquely backward and lateralward, the posterior 

 obliquely forward and lateralward; they unite in a thick tendon, which is inserted 

 into the deltoid prominence on the middle of the lateral side of the body of the 

 humerus. At its insertion the muscle gives off an expansion to the deep fascia of 

 the arm. This muscle is remarkably coarse in texture, and the arrangement of 

 its fibers is somewhat peculiar; the central portion of the muscle that is to say, 

 the part arising from the acromion consists of oblique fibers; these arise in a 

 bipenniform manner from the sides of the tendinous intersections, generally four 

 in number, which are attached above to the acromion and pass downward parallel 

 to one another in the substance of the muscle. The oblique fibers thus formed are 

 inserted into similar tendinous intersections, generally three in number, which 

 pass upward from the insertion of the muscle and alternate with the descending 

 septa. The portions of the muscle arising from the clavicle and spine of the scapula 

 are not arranged in this manner, but are inserted into the margins of the inferior 

 tendon. 



Variations. Large variations uncommon. More or less splitting common. Continuation into 

 the Trapezius; fusion with the Pectoralis major; additional slips from the vertebral border of the 

 scapula, infraspinous fascia and axillary border of scapula not uncommon. Insertion varies in 

 extent or rarely is prolonged to origin of Brachioradialis. 



Nerves. The Deltoideus is supplied by the fifth and sixth cervical through the axillary nerve. 



Actions. The Deltoideus raises the arm from the side, so as to bring it at right angles with 

 the trunk. Its anterior fibers, assisted by the Pectoralis major, draw the arm forward; and its 

 posterior fibers, aided by the Teres major and Latissimus dorsi, draw it backward. 



Subscapular Fascia (fascia Subscapularis). The subscapular fascia is a thin 

 membrane attached to the entire circumference of the subscapular fossa, and 

 affording attachment by its deep surface to some of the fibers of the Sub- 

 scapularis. 



The Subscapularis (Fig. 411) is a large triangular muscle which fills the sub- 

 scapular fossa, and arises from its medial two-thirds and from the lower two- 

 thirds of the groove on the axillary border of the bone. Some fibers arise from 

 tendinous laminae which intersect the muscle and are attached to ridges on the 

 bone; others from an aponeurosis, which separates the muscle from the Teres 

 major and the long head of the Triceps brachii. The fibers pass lateralward, 

 and, gradually converging, end in a tendon which is inserted into the lesser tubercle 

 of the humerus and the front of the capsule of the shoulder-joint. The tendon 

 of the muscle is separated from the neck of the scapula by a large bursa, which 

 communicates with the cavity of the shoulder-joint through an aperture in the 

 capsule. 



Nerves. The Subscapularis is supplied by the fifth and sixth cervical nerves through the 

 upper and lower subscapular nerves. 



Actions. The Subscapularis rotates the head of the humerus inward; when the arm is raised, 

 it draws the humerus forward and downward. It is a powerful defence to the front of the shoulder- 

 joint, preventing displacement of the head of the humerus. 



Supraspinatous Fascia (fascia supraspinata) . The supraspinatous fascia com- 

 pletes the osseofibrous case in which the Supraspinatus muscle is contained; it 

 affords attachment, by its deep surface, to some of the fibers of the muscle. It is 

 thick medially, but thinner laterally under the coracoacromial ligament. 



The Supraspinatus (Fig. 412) occupies the whole of the supraspinatous fossa, 

 arising from its medial two-thirds, and from the strong supraspinatous fascia. 

 The muscular fibers converge to a tendon, which crosses the upper part of the 





